Low voltage electric ignition system



April 18, 1961 B. H. SHORT LOW VOLTAGE ELECTRIC IGNITION SYSTEM Filed Sept. 12, 1958 ms r,

ID in INVENTOR. Brooks H. Short 7. H119 Attorney 2 ,980,823 LOW VOLTAGE ELECTRIC IGNITION SYSTEM Brooks H. Short, Anderson, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Sept. 12, 1958, Ser. No. 760,699

3 Claims. (Cl. 315-180) This invention relates to low voltage ignition systems of the type wherein a spark plug of the creepage gap or shunted surface type gap is fired by the ignition system. By low voltage system, it is meant that the spark plug may be fired at a potential in the neighborhood of 1500 to 2500 volts as compared to the usual 20 to 30 thousand volts required on conventional high voltage systems. Typical low voltage systems of this general typeare disclosed in the patents to Smits 2,125,035 and 2,478,672.

It is an object of this invention to provide a low voltage V ignition system wherein the voltage applied to the low voltage spark plug is controlled by an electronic circuit that alternately charges a condenser and then discharges the condenser through the low voltage plug.

Another object of this invention is to provide an improved power supply for a low voltage ignition system that has greater reliability and elficiency than those heretofore known.

A more specific object of this invention is to provide a low voltage creepage gap ignition circuit wherein the power for firing the creepage gap plug is derived from a power source that includes a transistor oscillator circuit.

Still another object of this invention is to provide a power source for a low voltage ignition system having output terminals connected with a transformer and wherein the secondary winding of the transformer supplies power to an ignition energizing circuit through one or more p-n junction diodes that may be of the silicon type.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

The single figure drawing illustrates an ignition system made in accordance with this invention.

Referring now to the drawing, the ignition circuit is adapted to periodically fire a spark plug 10 having one terminal connected with lead 12 and having another terminal 14 which is grounded. The lead 12 will contain the usual distributor mechanism (not shown) for supplying power'to a plurality of spark plugs. The spark plug 10 will be fired at low voltage, for example, somewhere in the neighborhood of 1500 to 2500 volts and is of the type commonly termed in the art as a creepage gap spark plug or a shunted surface gap spark plug. As an example, and not by way of limitation, the spark plug could be of the type illustrated in the patent to Smits 2,592,754. In the sort of ignition system to be described, the plug 10 thus will be fired at relatively low voltage as compared to the conventional high voltage systems wherein 20 to 30 thousand volts are required across the spark gap of the spark plug. 7

The ignition circuit has a power supply which includes a transistor oscillator circuit generally designated by reference numeral 16. The output of the transistor oscillator circuit is fed to the primary winding 22 of an iron core transformer generally designated by reference nu- 1C6 2,980,823 Patented Apr. 18, 1961 2 meral 20. The transformer has a secondary winding 18 which is center-tapped at 24 and which has a greater 1 number of turns than the primary winding to provide a.

predetermined step-up in voltage between primary and secondary. The transformer further includes a tertiary winding 26 which is center-tapped at 28.

The transistor oscillator circuit 16 includes a pair of transistors 30 and 32, each having a base electrode b,

collector electrode 0, and an emitter electrode e. The. emitter electrodes are connected with a junction 3 4 through resistors 36 and 38. The junction 34 is con nected with a lead 40 which is, in turn, connected with junction 42 and to one side of an ignition switch 43;

The opposite side of ignition switch 43 is connected to one side of a storage battery 44 which is thus connected between the switch 43 and ground as shown. The junc-f tion 42 is connected with the center tap of tertiary wind v ing 26, while the center tap of primary winding 22 is con nected directly to ground as shown. The base electrodes of transistors 30 and 32 are connected to opposite sides of tertiary winding 26 via resistors 45 and 46. A resistor 47 is connected between the junctions 48 and 49. Thecollector electrodes of transistors 30 and 32 are connected to opposite sides of primary winding 22 via leads 50 and 52. t

The secondary winding 18 of transformer 20 has a center tap 54 which is connected with lead 55. The op-' posite ends of the'secondary winding 18 are connected respectively with leads 56 and 57. The lead 57 is connected to the lower contact 58 of a relay generally designated by reference numeral 60. This relay includes an armature 62 which is normally biased by a spring 62a to engage a contact 63 during the time that the actuating coil- 64 of the relay is deenergized. The actuating coil 64 of the relay is connected between lead 65 and ground. The lead 65 is connected with contact 66 of a starting motor relay generally designated by reference numeral 67. This relay includes a movable switch contactor 68 which cooperates with fixed contacts 66, 69 and 70. The switch contactor 68 normally is out of engagement with the fixed contacts and is pulled into engagement with these contacts when the actuating coil 71 is energized. It is seen that actuating coil 71 is connected between ground and a side of electric starting motor 76 via lead 77. The starting motor is, of course, adapted to crank the engine of the motor vehicle whenever it is energized and it is connected between ground and relay contact 70. The fixed contact 69 of relay 67 is connected with ,ajunction 79 via lead 78.

The relay actuating coil 64 operates to control the movement of an armature 80 which periodically engages fixed contacts 81 and 82. The armature 80 is normally held in its position contacting switch contact 82 by a spring 83. When the relay coil 64 is energized, the armature 80 will be moved to engage switch contact 81 and will also move armature 62 to engage switch contact 58. It, thus, is apparent that the relay actuating coil 64 op crates to control movement of both armatures 62 and 80. The contacts 81 and 82 are connected to tap points 84 and 85 on potentiometer 75. The potentiometer has its opposite ends connected respectively with lead 73 and ground.

The armature 62 of relay 60 is electrically connected with a lead 86 which is, in turn, connected with junction 87. The lead 56 is connected with a junction 88 which is, in turn, connected with lead 89. A'p-n junction semiconductor rectifier 90, which may be of the silicon type, is connected between junctions 88 and 91 and a second p-n junction diode 92 is connected between lead 89 and junction 93. A condenser 94 is connected between junctions 91 and. 87 and a. second' condenser" 9;5.is connected betweenjunctionsi 87 and93; The pm junction diodes arepreferably of. the silicon. t-ype com-- 97. The, opposite side of the inductance is connected with av junction 98 which is, in turn, connected with leads 99 and 100. A condenser 102 is connected be tween; junctions 98.- and 104, the junction. 104 being connecte'd to lead 12. The lead 100 is connected with a junction 106 which is, in turn, connected with a lead wire, 108 that connects. junctions 93 and 106.

A. transformer. generally designated by reference. numeral 1 has. a primary. winding 112 connected with armature 80 and has a secondary winding 114 connected with junction 117. The junction 116 is connected. to one sideof a pair of breaker contacts 118 which are opened aesdeasandrclosed by a cam 120 driven in synchronism with the engine of the motor vehicle. These breaker contacts form a part of the well-known motor vehicle distributor and it is seen that they are connected between junction 116-and ground. An electronic switch which takes the form of. a gas filled thyratron tube 122 has its cathode connected with lead99- and has a plate connected directly to; ground via lead 124. The grid of this tube is connected with a lead 126 and thus is connected with the secondary winding 114 through a resistor 128.

=ln operation, an operator desiring to start the motor vehicle engine closes the switches 43 and 72. The closure of switch 72.energizes the relay coil 71 to cause a shorting together of contacts 66, 69 and.70. The starting motor 72 will thenrbe energized from contact 70 whereasthe relay coil,64 wi ll be energized from contact 66. When. relayv coil.64 is energized, it causes thearmature 62 to contact switch contact 58 and causes armature. 80; to engageswitch contact 81'. It-thus is seen that theentire voltage developed across. secondary winding 18 will be supplied between junctions 87 and 88 while the voltage appearing,

between tap point 84 andground of potentiometer 75 wil l ,be impressed across the primary winding 112 of transformer 110. It thus can be seen that, when the starting motor 76 is energized, the armatures 62 and 80 aremoved to increase the apparent energization of certain. of the ignition circuits. This has a compensating efiect on the ignition circuit as the energization of starting motor 76 will drop the output voltage of the battery 44 and this is compensated for by the switching operations. just described. During the time that the engine is 4. resistance and coil primary inductance. When the current on the second side of the transformer has reached a predetermined value, the tertiary winding shuts ofi the transistor 32 and brings the transistor 30 back into conduction. In this way, the transistor oscillator operates as a self-excited generator of alternating current which may have afrequency in: the neighborhood of 20,000 cycles per second. The transistor oscillator circuit thus supplies the primary winding 22 with an AC. voltage that is stepped up by the transformer and which. appears as a higher voltage across the secondary winding 18. The transistor oscillator circuit may be termed a flip-flop oscillator circuit as the transistorsare rendered alternately conducting and nonconducting with only one transistor being turned on at a time.

The AC. voltage appearing at the end terminals of secondary winding 18is: rectified by. silicon diodes 90 and 92. It will be appreciated thatthe connections of the silicon diodes with. the transformerv and with the coudensers: 94 and 95 provide a voltage doubler circuit and that this. direct current. voltage will. appear between junctions 91 and 93 as: determinedby. the voltage doubler circuit. The voltage. appearing between junctions. 91 and 93: is usedto. cause. the:- firing of spark plug 10..

When the breaker contacts 118 are in a closed'position, current flows through. primary winding 112 of transformer 110 to ground. and currentis also-permitted to flow. through inductance 97 and. through condenser 102 to charge the condenser. This circuit may be traced from lead 91, through; silicon diode. 96,.through inducttime 97, through condenser 102Jto junction 1.94; and thence. throughlead-108 to junction. 93.- Thus; during the time that. thebreaker. contacts are closed, current is being built up in both the primary winding. 112 and a charge is1being developed-on condenser 102. When the breaker contacts118 open, a high. voltage. is developed in secondaryfiwinding; 114;; of transformer 1'10'which is of such a" polarity asto biasthethyratron.tube; 122 into its conductive state. WithIthyratron tube 122 conducting, the condenser. 102;discharges1 through a circuit that includesthe thyratron. tube. 122; and the shunted surface operating, the relay armature 62 and 80 will be in the positions illustrated in the drawing to supply normal voltagestotheir respective circuits.

The closure of ignition switch 43 connects one side of the battery with junction 34 and renders the transistor 30 conductive from the emitter to collector. This current flows through one half of the primary winding 22 and through the resistor 36. The current that flows through onehalf of the primary winding 22 allows fiux to be set up in the core of the transformer. This current grows at a-rate determined by the total circuit resistance and the self-inductance of one half of the primary winding. The flux in the core is accompanied by a. corresponding voltage in the tertiary windings of the transformer. This voltage causes the transistor 30 that was conducting to be turned off and turns on the transistor 32. When transistor 32 has been rendered conduct i g, current is allowed to fiow through its half of pri:

gap-spark.plug.10.'. This circuit: may be traced from the top side of condenser. 102;.through junction98, through thyratrontube' 122, through spark pluglO and thence through lead 12' back. tozjunction. 104. The condenser will be charged; toavoltage .in the neighborhood of 1500 to 2500 volts and this voltage is sufiicient to cause the firing of spark plug ltli'when the condenser 18?. discharges.

The particular circuit just describedis highly efficient in that the [in junctiom semiconductor rectifiers have very low voltage drops: aszcompared with other types of rectifiers. Inaddition, the transistors of the transistor oscillator have no movingpartslso that thepower supply is not subject todestruction. as. are power supplies that employvibrators and thelike. The: circuit has the further advantage in that the transistors may be operated by the voltage available on the motor vehicle which commoniy is 12 volts. By the use of transistor oscillator, the ire quencies-employed arehigh as compared with other types of power packsand, thus, thesizeof the transformer 20 may begreatly reduced as compared to-other heretofore known ignitionsystejms.

While the embodiments oi the present invention as herein disclosed constitute preferred forms, it: is to be understood that other forms might be adopted.

What is claimed is' 'asfollows:.

1; A lowvoltageel'ectronic ignition system for igniting the combustible mixture in an internal combustionengine comprising," a'- relatively lowsvoltagebattery, a relatively highfre'quency oscillator circuitincluding at least one transistor; means connecting said oscillator circuit tobe energized :by'saidlow voitagebattery, transformer means including a secondarywinding" energized from saidas cillator circuit for boosting the A.C. voltage developed by said oscillator circuit, rectifier means of the PN junction semiconductor type connected with said secondary Winding for converting the high frequency A.C. output of said oscillator circuit to direct current, a condenser, a spark plug of the creepage gap type, means connecting said condenser and the electrodes of said spark plug in series with each other, means connecting said condenser with said rectifier means whereby said condenser is charged with direct current, a three terminal electronic switch having a pair of current carrying terminals and a control terminal, a discharging circuit for said condenser including the current carrying terminals of said electronic switch and said creepage gap spark plug, and means connected with the control electrode of said electronic switch for controlling the conduction of said electronic switch in synchronism with operation of said engine, said last named means including breaker contacts energized solely from said low voltage battery.

2. A low voltage electronic ignition system for igniting the combustible mixture in an internal combustion engine comprising, a relatively low voltage battery, a relatively high frequency oscillator circuit including at least one transistor, means connecting said oscillator circuit to be energized by said low voltage battery, transformer means including a secondary winding energized from said oscillator circuit for boosting the A.C. voltage developed by said oscillatorcircuit, rectifier means connected with said secondary winding for converting the 'high frequency A.C. output of said oscillator circuit to direct current, a condenser, a spark plug of the creepage gap type, means connecting said condenser and the electrodes of said spark plug in series with each other, means connecting said condenser with said rectifier means whereby said condenser is charged with direct current,

a three terminal electronic switch having a pair of current carrying terminals and a control terminal, a dis.- charging circuit for said condenser including the current carrying terminals of said electronic switch and said creepage gap spark plug, and means connected with the control electrode of said electronic switch for controlling the conduction of said electronic switch in synchronism with operation of said engine, said last named means including breaker contacts energized solely from said low voltage battery.

3. A low voltage electronic ignition system for igniting the combustible mixture in an internal combustion engine comprising, a relatively low voltage battery a relatively high frequency oscillator circuit including at least one transistor, means connecting said oscillator circuit to be energized by said low voltage battery, transformer means including a secondary winding energized from said oscillator circuit for boosting the A.C. voltage developed by said oscillator circuit, rectifier means connected with said secondary winding for converting the high frequency A.C. output of said oscillator circuitto direct current, a condenser, a spark plug of the creepage gap type, means connecting said condenser and the electrodes of said spark plug in series with each other, means connecting said condenser with' said rectifier means whereby said condenser is charged with direct current, a three terminal electronic switch having a pair of current carrying terminals and a control terminal, a discharging circuit for said condenser including the current carrying terminals of said electronic switch and said creepage gap spark plug, and means connected with the control electrode of said electronic switch for controlling-the conduction of said electronic switch in synchronism with operation of said engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,519,776 McNulty Aug. 22, 1950 2,662,202 Short. Dec. 8, 1953 2,826,731 Paynter Mar. 11, 1958 2,833,963 Tognola May 6, 1958 2,843,815 Driver July 15, 1958 

